Suggestion on integrating form membership plugin

I’ve been trying to look for a solution and haven’t had any luck so I’d like to ask for suggestions.

What I need to do is offer private members only content so I’d like to set my site up so that members have to register to access certain content. But what’s equally important to me is to get them to fill out a specific form that has certain questions that the membership plugins don’t include.

I tried adding a form into the registration page, but that doesn’t work well because they would have to hit two different submit buttons. I could get them to fill out a form and then have an autoresponder direct them to the registration page…

Ideally, I’d like to have the user just fill out one form that will register them for the free membership and will also let me add in custom questions in the form. Does anything like this exist? thanks!